The present invention generally relates to a device for performing a surface treatment on semiconductor wafers.
U.S. Pat. No. 5,958,146 discloses an ultra-low particle semiconductor cleaner using heated fluids. In general, a surface treatment on semiconductor wafers is known wherein water is removed from the major surfaces of the wafers by directing isopropanol alcohol mixed with nitrogen gas onto the surfaces (also referred to as IPA treatment). Due surface adhesion effects, the isopropanol alcohol occupies major surfaces, expels water and finally evaporates. In other words, as water recedes, it gets displaced with a thin film of isopropanol alcohol vapor and nitrogen mixture.
FIG. 1 illustrates a known device for performing a surface treatment on semiconductor wafers. In FIG. 1, reference sign 1 denotes a wafer cassette. The wafer cassette 1 is designed for accommodating a plurality of semiconductor wafers 5 in its interior 3, wafers 5 have major surfaces 51. In the interior 3 of cassette 1, there are grooves which are not shown and which are designed for receiving wafers 5 such that wafers 5 are aligned in a row having their major surfaces 51 essentially in parallel with each other.
Moreover, the cassette 1 comprises a top lid 10 which is pivotably hinged by a hinge indicated with reference sign 4. In top lid 10 there are supply channels 12, 13, 15 for transporting a surface treatment medium, here a mixture of isopropanol alcohol and nitrogen in gaseous state, from a feeding point FP (see FIG. 2) to openings 121 to 124 and 131 to 134 which are provided on the face 101 of the top lid 10 which is directed to the semiconductor wafers. Thus, the surface treatment medium supplied via the feeding point FP to the supply channels 12, 13, 15 is distributed over wafers 5 via openings provided in supply channels 12 and 13, respectively.
Moreover, reference sign 20 in FIG. 1 denotes an IPA bubbler, which is fed with IPA by supply line 27 and with nitrogen by supply line 25. Reference sign 28 denotes an exhaust line, and 29 denotes a feeding line for transporting the IPA/nitrogen mixture to feeding point FP.
FIG. 2 illustrates a magnified view of the known device for performing a surface treatment on semiconductor wafers of FIG. 1 for illustrating the top lid thereof. FIG. 2 shows a view on to top lid 10 from above. As becomes apparent from FIG. 2, supply channels 12, 13 each comprise a plurality of openings 121 to 124 and 131 to 134, respectively, which in this example are formed as circular openings. Feeding point FP which introduces the surface treatment medium from above is arranged in the middle of supply channel 15 which connects supply channels 12 and 13. In this example, feeding point FP is arranged asymmetrically with respect to supply channels 12, 13. In other words, the openings 121, 131 and one of supply channels 12, 13 are more distant from feeding point FP than openings 124, 134 at the other end of supply channels 12, 13. Moreover, in this design all openings 121 to 124 and 131 to 134 have the same geometrical size. Furthermore, supply channels 12, 13 have a rather narrow span which is much smaller than the diameter of a wafer 5 which is schematically indicated by the dashed line in FIG. 2.
With the known device shown in FIG. 2 incomplete water removal from the wafer surfaces and formation of high particles due to lack of non-uniform IPA flow and delivery in front and back of the cassette constitutes a serious problem. In particular, at present this problem has to be obviated by running 40 wafers instead of possible 50 wafers in cassette 1.
Since the known IPA manifold of FIG. 2 neither delivered uniformly nor sufficiently, the water might be removed incompletely from the wafer major surfaces and hence forms water marks on hydrophobic surface which might show up as particles and therefore detracts the process yield. The current IPA holes in the rows are of the same size along the rows and this creates different pressures along the rows. As a consequence, the flow rate of the surface treatment medium of holes having a different distance from the feeding point is different, namely the flow rate decreases with increasing distance from the feeding point.
The present invention seeks to provide to a device for performing a surface treatment on semiconductor wafers which mitigates or avoids these and other disadvantages and limitations of the prior art.